Efreet Flamepainter

• WOTC Official Reminder Textofficial rules
  Double strike — This creature deals both first strike and regular combat damage.

• WWizards of the Coast2021-04-16
  Official Ruling
  If you cast a spell “without paying its mana cost,” you can’t choose to cast it for any alternative costs. You can, however, pay additional costs. If the spell has any mandatory additional costs, those must be paid to cast the spell.
• WWizards of the Coast2021-04-16
  Official Ruling
  If the card has in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
• WWizards of the Coast2021-04-16
  Official Ruling
  Efreet Flamepainter’s triggered ability lets you cast the spell immediately, ignoring timing restrictions. It doesn’t let you choose to cast it at a later time.

Rulings via Scryfall